What is the purpose of ?? Null Coalescing Operator in C#?

In this post, we will be learning about the null coalescing operator in C# with help of an example code snippet.

Introduction

The ?? operator is called the null coalescing operator. It returns the left-hand operand if the operand is not null otherwise, it returns the right-hand operand.

You might already know that C# 2.0 provides us Nullable Types that can be used to store null values for value type variables such as int, float, decimal, etc.

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For example, let’s consider the following code snippet.

int? x = null;            
int y = x ?? 0;
Console.WriteLine(y);

In the above example, x is a nullable int and if you assign it to the non-nullable int y then it will throw a runtime exception if x is null.

Purpose of ?? Null Coalescing Operator in C#

Well, ?? provides a convenient way to assign a nullable type to a non-nullable type.

int y = x ?? 0;

It saves us having to write code that tests for null and sets a value appropriately. The above statement sets the value of y to the value of x unless the value in x is null, in which case it sets it to 0.

if (x == null)
    y = 0;
else
    y = x;

In other words ?? is a short form of the above test.

The result of a ?? operator is not considered to be constant even if both its arguments are constants.

Null Coalescing Operator in C#

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To read more on ?? operator you may refer 👉 ?? Operator in C#

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